Re: gEDA-user: capacitors

[Dan McMahill <dan@xxxxxxxxxxxx>]

Marc Price wrote:
> Im wondering what i can use instead of Electrolytic capacitors, what is 
> high quality  high stability polarised capacitor at value of 0.01uf
>
> any ideas pls
>
> Marc :)

for 0.01 uF I don't know why you'd use an electrolytic at all (or any 
other polarized cap like a tantalum).  You can probably get a 0.01uF in 
a package as small as 0201 (for low voltage) in a ceramic.

Now, the real question is what exactly do you mean by "high quality" and 
"high stability".

Do you mean high quality factor (i.e. low loss)?

Do you mean high linearity (low voltage coefficient)?

Low leakage?

Stable vs temperature?

Accurate initial capacitance?  How accurate?

Again, at 0.01 uF, I'd avoid electrolytics (if you can even get them 
that low).  Aluminum electolytics suck all around.  Low lifetime, leaky, 
_noisy_ (yes indeed, the leakage current in an electrolytic is noisy), 
etc.  Probably what you want is a ceramic, but watch out.  I've measured 
some audio circuits where the dominant distortion mechanism was the 
ceramic caps.  Replacing them with paper caps dropped the distortion by 
at least 20 dB, maybe more.  Of course that will depend on what you're 
using them for.  Ceramics in an audio filter or oscillator are more 
critical for linearity than in an AC coupling application.

Enough questions for your question?

-Dan